1. Technical Field
The present invention relates generally to rack mountable communication system housings that contain integrated circuitry; and more particularly to the manner of construct of such communication system housings.
2. Description of the Related Art
Communication systems are well known. Communication systems have existed in many forms for quite some time. For example, the public switched telephone network (PSTN) has been in widespread use for many decades. The PSTN is a circuit switched communication network in which communications share time divided bandwidth. Such a circuit switched network is contrasted to the Internet, for example, which is a packet switched network. In packet switched networks, all communications are packetized and transmitted in a packetized format from a source to a destination.
Communication systems include a large number of switches coupled by communication links. The switches include integrated circuitry that performs storage and routing functions for the communications. The communication links may be physical media, e.g., optical fiber, copper, etc. The communication links may also be wireless, e.g., microwave links, satellites links, radio links, etc.
As communication demands have been ever increasing, the loads placed upon both the communication switches and the communication links have also increased. Thus, higher capacity switches and higher capacity communication links have been created to meet these demands. With the wide scale miniaturization of integrated circuits, switches can now be constructed to provide high volume switching but be contained in a relatively small housing. Further, with the development of media such as optical fiber, the communication links are capable of carrying significant levels of communications between switches.
Communication system switches, as is also well known, may be high-speed carrier network switches that handle a huge amount of traffic or may be smaller switches, which carry lesser volumes of traffic. The amount of traffic that can be carried by a switch depends upon not only upon the number and bandwidth of communication links coupled to the switch but the processing capabilities of the switch itself. Thus, to increase the processing capabilities of the switch, it is important to place all components of the switch into a small area to decrease the size of the switch.
As switches become ever smaller they experience significant operational problems. For example, it is desirable to construct switches such that they have a minimum footprint size. Further, it is desirable to modularize the switches into components. Thus, most switches are typically constructed to include a plurality of rack mounted switch components/housings, each of which performs a portion of the operations of the switch. These rack mounted switch components are placed vertically with respect to one another. Each of the switch components couples to physical media that forms a communication link and also couples to a back plane of the rack so that the switch component may route traffic to and from other switch components. This rack-mounted structure therefore provides great efficiencies in reducing the footprint size of the overall switch and also allows a number of switch components to be efficiently coupled to one another. Switching functions may be divided between the switch components to produce greater throughput and for backup/fail over purposes.
However, each switch component produces a large amount of heat because the switch component includes a large number of integrated circuits, each of which produces significant heat. Thus, cooling of the integrated circuits within the switch components is a difficult task. When this task is not properly accomplished, the integrated circuits on the switch components fail causing the overall capacity of the switch to decrease and may cause disruption in the communication path that includes the switch component.
A further difficulty in such a rack mounted switch configuration is that the integrated circuits themselves produce electromagnetic interference (EMI). This EMI may be large enough to interfere with other integrated circuits within the switch components of the rack and even to cause disruption in the back plane coupling the switch components. Further, the Federal Communications Commission limits the amount of EMI energy that may be produced by devices of this type. Thus, it is important to either design the switch components to minimize EMI or to provide adequate shielding for the switch components.
Each of the switch components physically includes a circuit board upon which the plurality of integrated circuits is mounted. Coupled to this printed circuit board is a physical media, e.g., optical fiber media. Because of the space limitations for the rack mounted switch components, it is desirable to minimize the overall depth of the switch component. However, in conventional rack mounted switch components, the optical fiber media is inserted perpendicular to the face of the rack mounted switch components. This type of mounting increases the depth of the switch component and often results in unintentional bending of, and damage to the optical fiber media.
Additional difficulties relate to the structure of printed circuit boards that reside within the switch components. Each switch component typically includes at least one circuit board that provides the switching functionality for the switch component. These circuit boards fit within a housing that has a predetermined size and that is received within a rack. Disposed on each circuit board are a plurality of integrated circuits, termination points for physical media, and a connector that couples the circuit board to the back plane of a rack in which a respective housing mounts. When any components of the circuit board fail, the circuit board must be removed from the housing and replaced with an operational circuit board. During this replacement operation, the switching functionality of the circuit board is lost. Thus, redundancies are built into the circuit boards, e.g., parallel media connection points that couple to parallel media, that cause the circuit board to provide its functions even when one component fails, e.g., a media coupler. However, such redundancy does not address problems caused by the failure of integrated circuits upon the circuit board. In such case, the circuit board must be fully removed to replace the circuit board with a fully functioning circuit board.
Traditional Telecom rack assemblies are made to hold rack sub-assemblies having a twenty-three inch form factor. Stated differently, the width of a traditional Telecom sub-assembly is twenty-three inches in width. Lately, however, there is a trend to utilize sub-assemblies having a nineteen-inch form factor. Accordingly, vendors of sub-assemblies typically make both nineteen inch and twenty-three inch sub-assembly products according to the requirements of the telecommunication service providers.
From the telecommunication service provider""s perspective, it must determine whether to go with a particular nineteen inch or twenty three inch sub-assembly according to a plurality of considerations including available space for nineteen or twenty three inch racks and, also, the space within the racks it presently owns or plans to acquire. Thus, logistic issues and space availability considerations may often drive equipment purchase decisions..
Another issue relating that should be considered is that twenty-three inch sub-assembly systems are traditionally made to conduct exhaust from cooling air out of a backside of the sub-assembly. Some sub-assemblies, however, are made to conduct exhaust from cooling air out of one of its two side panels. Accordingly, a nineteen-inch sub-assembly cannot be made to merely fit within a twenty-three inch rack without violating traditional air exhaust port placement.
These shortcomings, among a great other remain unaddressed by a prior art rack mounted communication system components. Thus, there is a need in the art for improvements in such rack mounted communication system components.
The present invention provides a rack mount extension that is formed to conduct cooling air exhaust received from a nineteen-inch sub-assembly side panel to a rear exhaust port. The rack extension is formed to attach to the sub-assembly and to enable it to be installed into a rack having a twenty-three inch form factor. The rack-mountable system further forms an enclosure for limiting the escape of internally generated electromagnetic interference and includes a system case, a front panel, a back panel, overlapped seams formed to couple the front panel and the back panel to the system case such that no gaskets and a minimal number of fasteners arc required, and at least one front opening through which communication media passes and apertures formed within the system case for providing air inlet and egress ports. The system enclosure further defines a first volume that receives a cooling fan module, a second volume that receives a plurality of integrated circuit boards, and a third volume through which cooling air exits.